The present invention relates to improvements in mechanisms for the preparation of mineral mixtures, particularly of a rough washed coal in a jig controlled by compressed air wherein the liquid mixture of the coal is given a pulsed motion by means of pulsations of compressed air, and the invention particularly relates to an improved valve structure for controlling the air pulsations.
In wet jigging machines for preparing coal or other minerals, it is customary to employ a plurality of pulse chambers which may open downwardly beneath the surface of the liquid and the chambers are supplied with air pulsations at a controlled frequency. In a control of these pulsations, both for the supply of compressed air and the release of air to the atmosphere, the valves that have been used conventionally employ rotary slide valves or disk or mushroom poppet type valves. An example of a control arrangement is shown and described in U.S. Pat. No. 4,019,981.
An object of the present invention is to provide an improved valve construction and operation which avoids disadvantages present in valves heretofore available such as rotary slide valves and which allows for a better and individual control of the pulsed air. A further object is to provide a valve arrangement which avoids disadvantages present with disk or poppet type valves. An object is to provide a valve structure which is less complicated, obtains individual control of a pulsed air and requires no actuation compressed air system so that the conventional supply of compressed air may be used for operation. A mechanical structure should be as simple as possible, and the drive or operation mechanism for the valve should operate essentially free of wear and not require maintenance or repair.
In accordance with the principles of the invention, the control of the pulsed air utilizes a pivoted butterfly valve mounted on a central pivotal shaft wherein the valve functions quickly and moves with a low operating force and attains characteristics which are as good as or better than known poppet or slide valves. A further feature of the invention is the provision of the shaft with a butterfly valve with an extension which carries a swing flap or wing that is pneumatically or hydraulically moved to operate the valve. By providing a swing flap on the shaft which has a variable range of swing movement, a very compact valve unit is obtained with the operating power derived directly from the valve support shaft with the most direct response. With this structure, the drive by variable movement swing flap, the drive is superior to and simpler than a drive such as which employs a piston and a piston rod. Friction losses in the transmission of power are elimiated. The work can be carried out with the lowest amount of energy required, and the amount of mass to move with each movement of the valve is maintained very low.
A further feature of the invention is that the butterfly valve employs a multi-part seat formed of an elastomeric material, preferably rubber. With the elastomeric seat, minimum wear occurs between the valve and seat and a further advantage is attained in automatic damping of the valve closing. Further, the arrangement attains an advantage in that a part of the kinetic energy of the movement of the butterfly valve is stored in the elastomeric seat so that the reverse movement of the valve is augmented.
A further feature of the invention is the provision of a seat which is located in a conduit for the valve which has a larger outside diameter than the butterfly valve. Thus, the possible friction of the butterfly valve against the outside wall of the conduit is eliminated so that no breakaway force need be exerted when opening the butterly valve.
In a preferred arrangement, the butterfly valve is constructed with interconnected multiple plates which are preferably welded to each other. In this fabricated construction, the strength of the butterfly valve can be augmented, but its weight can be significantly reduced in comparison with a valve that has a onepiece solid structure and with equal actuating forces, more rapid movement of the butterfly valve is possible.
A further feature of the invention resides in providing a butterfly valve which is eccentrically connected to the shaft so that unequal areas face upstream toward the compressed air. The portion of the valve which moves against the seat facing upstream is of a larger area so that the balance of air forces tends to close the valve against its seat which improves the operation of the valve.
A further improvement resides in the operator for the valve which includes a variable movement swing flap which is located in contact-free relationship within a housing or chamber. The housing or chamber receives compressed air, controlled by an operating valve and supplied by the same source of compressed air which pulses the liquid. With this arrangement, no wear occurs in the operator, and the speed and forces required of the operator are not changed due to wear of the sealing elements. In accordance with the construction, a clearance or gap of 0.05 to 0.1 mm between the swing flap and the housing has been found to leave an air loss which is not significant in the operation of the valve using the standard source of compressed air as the working air which has a pressure of approximately 1.5 bar, and the loss of approximately 1 liter per second can be readily tolerated in the system.
The variable movement swing flap is constructed of mutually connected welded sheet metal plates which engage an elastic stop preferably in the form of an adjustable rubber cone in the open position of the valve. This rubber stop dampens the movement of the valve in the opening direction and also provides for the storage of kinetic energy of valve movement so that the characteristic of the valve in its closing movement against its elastomeric seat is obtained in the movement of the valve in opening direction by the elastomeric stop for the swing flap. The movement of the swing flap is gently decelerated and damped as the open position is reached, and a part of the kinetic energy is stored. Thus, overall a butterfly valve drive unit which functions quietly and which is rugged and functions reliably with a low energy requirement is attained.
It is a further feature of the invention that the butterfly valve, a pivot shaft and the variable swing flap form a mutually connected unit which can be commonly removed. Thus, an advantageous unitary design of the valve and drive is possible which enables very rapid replacement upon the occurrence of a malfunction. Replacement valve blocks can be kept on hand as standard components and can advantageously be repaired and maintained in the shops. This enhances the continued operation and reliability of the jigging machine.
A further advantage of the invention is that the operator in the form of the variable swing flap is actuated by the same source of air which is used for the pulsations. This provides that a separate compressed air system is not necessary and separate mechanical drives are not necessary.
As a result of the unitary structure and the use of pulsed air as the drive for the valve operator, it is possible to completely house the valves together with their drives in the compressed air chamber located upstream of the valves. This further attains a jigging machine which is compact and which can be constructed more compactly than valve arrangements heretofore available.